The data signal coherence check by the data processing unit may be applied to any type of receiver, even for direct reception of an unprocessed data signal on a channel or in a wired manner. This data signal is generally defined by a sequence of bits over time. “Data coherence” essentially means the reliability of the modulated or non-modulated data, picked up by the signal receiver.
Usually a digital radio frequency receiver produces a demodulated data signal at the output of a demodulator, when the data is extracted from the incoming radio frequency signals, which were transmitted by a transmitter. Data modulation in the radio frequency signals on the carrier frequency may be of various types. It may be frequency shift keying (FSK), amplitude shift keying (ASK) or ON-OFF keying (OOK).
In a conventional receiver, there are several steps to determine whether the information contained in the received radio frequency signals is deemed suitable, i.e. the data is correct and can be used by the receiver. If the frequency of the received radio frequency signals is first of all converted via at least one mixer unit and by means of oscillating signals from a local oscillator, the frequency of the intermediate signal at the mixer unit output must be within a specific frequency range. The strength or power of the received radio frequency signals must also be greater than a noise level, which characterises the receiver. The strength or power may be checked via a received signal strength indicator. An error calculation may also be carried out after data demodulation on the basis of the demodulated data signal, when the data is processed in the receiver. This error calculation must provide a value lower than a defined threshold (CRC).
Subsequently, the receiver must also synchronise the data clock with the local clock thereof on the basis of the data signal. This must be done to enable the data in the radio frequency signals picked up by the receiver to be digitally processed. Generally, with this type of conventional receiver, complete data pack acquisition is performed taking account of correct data transitions in the data signals. An error calculation of all the data may be carried out as indicated hereinbefore. If it is observed that the data in the received radio frequency signals is not correct after all the data processing, everything is then reset to enable the receiver to pick up other radio frequency signals. This constitutes a drawback, since there must therefore be a long period of processing all the data before the receiver is reset if the data is incorrect.